The addition of a proportion of Recycled Asphalt (RAP) to the final formula has become standard practice
Road builders are seeking ever-higher recycling rates – not just to preserve natural resources but also to optimise production costs thanks to the aggregate and bitumen savings resulting from the use of modern recycling techniques.
Advanced recycling ring
The cold recycled material is added directly into the dryer mixer via a special recycling ring and is brought up to the final temperature by a heat exchange with the overheated virgin aggregates.
The advanced design of the recycling ring prevents any clogging that could arise during the gradual fusion of the residual bitumen contained within the materials to be recycled.
This economical, fully tried and tested solution allows for high recycling rates of up to 35% or even more in specific circumstances.
As the RAP and virgin aggregates are brought into contact upstream of the screen, the granular blending must be managed at the cold feed bin level. Additional weight-based metering systems may then be used to good effect in order to guarantee optimal metering quality.
Recycling in the mixer
The recycled materials are conveyed to the mixer by a cold-mix elevator and, like the virgin aggregates, are metered in a dedicated weighing hopper before being added to the mixer.
The steam released in the mixer must be removed and the production output may be modified in order to ensure a complete heat exchange between the cold RAP and the heated virgin aggregates.
As the virgin and recycled aggregates follow different circuits through to the mixer, the virgin aggregates can be screened. Recycling rates of up to 25% may be achieved and, by combining this technique with a recycling ring, rates of 40% or more are possible in specific circumstances.
Recycling in a second dryer drum
The recycled materials are dried and heated in a dedicated parallel-flow dryer drum especially designed for this purpose. The internal flights thus allow the recycled materials to be gradually brought up to temperature and avoid any risk of clogging, which allows for the achievement of high recycling rates of 60% or more. The virgin aggregates follow the conventional circuit and are screened.